Re: [Xen-devel] [PATCH] tools/firmware: update OVMF Makefile

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Wed, Jan 09, 2019 at 07:56:59AM -0700, Tamas K Lengyel wrote:
> On Wed, Jan 9, 2019 at 7:56 AM Tamas K Lengyel
> <tamas.k.lengyel@xxxxxxxxx> wrote:
> >
> > On Wed, Nov 28, 2018 at 10:44 AM Wei Liu <wei.liu2@xxxxxxxxxx> wrote:
> > >
> > > OVMF has become dependent on OpenSSL, which it is included as a submodule.
> > > Initialise submodules before building.
> >
> > If you are updating the ovmf makefile, could you by any chance also
> > make the debug build of it more useful on Xen by making it print to
> > the Xen console? Needs the -D DEBUG_ON_SERIAL_PORT flag added and the
> > following one-liner to change it to correct port:
> >
> > sed -i 's/PcdDebugIoPort|0xe9/PcdDebugIoPort|0x402/g' OvmfPkg/OvmfPkg.dec
> >
> 
> Whops, actually the other way around for sed:
> 
> sed -i 's/PcdDebugIoPort|0x402/PcdDebugIoPort|0xe9/g' OvmfPkg/OvmfPkg.dec

You can actually have OVMF debug output without rebuilding it, add this
to our VM config:
device_model_args_hvm = [
  # Debug OVMF
  '-chardev', 
'file,id=debugcon,mux=on,path=/var/log/xen/qemu-dm-ovmf.log.debugcon,',
  '-device', 'isa-debugcon,iobase=0x402,chardev=debugcon',
]

That way OVMF boot isn't slow down by writing to an ioport if there
isn't someone to care.

The way you suggest will have OVMF write to an ioport that the Xen
hypervisor will then write to it's console (or xl dmesg) and with the
amount of debug that ovmf write, this is quite slow. And worse, that
isn't going to work anymore with upstream OVMF as it now check if there
is something to listen on the other side of the ioport, Xen isn't going
answer the right things and OVMF will stay silence. (That paragraph is
about the change of PcdDebugIoPort.)

I don't know if DEBUG_ON_SERIAL_PORT is going to work, and how it works,
but it certainly don't use PcdDebugIoPort. Using a serial port instead
of an IO port is even going to be slower. So I don't know if it would be
useful to have.

-- 
Anthony PERARD

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